Thermoplastic carbonate polymers are readily molded at elevated temperatures to make a wide variety of articles such as automotive parts, tool housings and similar structural components. However, carbonate polymers have a number of deficiencies which tend to limit their use, including sensitivity of impact resistance to the ambient temperature, a relatively high processing temperature and susceptibility to degradation by solvents including water and hydrocarbons. Therefore, there have been numerous attempts to overcome or compensate for the deficiencies of carbonate polymers by blending them with one or more other polymeric additives.
Thermoplastic polyurethanes when used at low levels (less than 30 weight percent) are known to have an impact modification effect and to improve the toughness of rigid polycarbonates. At higher levels of TPU, however, little additional improvement in toughness is obtained, particularly in the low temperature toughness which is needed for a variety of applications such as automotive parts. Additional amounts of an impact modifier would therefore not be expected to serve to improve the low temperature toughness of PC/TPU blends.
For example, U.S. Pat. No. 4,743,650 discloses binary blends containing polycarbonate and from 5 to about 35 parts by weight of a polyether-based thermoplastic polyurethane ("TPU"). U.S. Pat. No. 4,179,479 discloses similar blends containing polycarbonate, from 40 to 100 parts TPU and a processing aid. However, due to the inherent problems of compatibility between polycarbonate and TPU, which include large differences in melt viscosities, processing temperatures and thermodynamic solubilities, the preparation of blends of TPU and polycarbonate having good combinations of toughness (especially at low temperature), heat resistance, solvent resistance and processability has not been accomplished.
In certain outdoor applications, such as automotive applications, it would be desirable to employ thermoplastic blend resins due to their light weight and resistance to rusting. However these advantages together with their excellent balance of physical properties at standard temperatures of 0.degree. F. and above were outweighed by their brittle failure at low temperatures of -10.degree. F. and below. Accordingly, it would be desirable to provide an improved blend of carbonate polymer and TPU with an improved balance of low flexural modulus, heat resistance, solvent resistance and toughness while maintaining an efficient level of processability. This would provide highly desirable thermoplastic resins which can be used in more demanding applications.
For example, for the preparation of thermoplastic automobile bumper facia or similar parts for outdoor applications it is important for the thermoplastic resin part to possess (a) good flexibility as exhibited by a flexural modulus value of less than about 200,000 pounds per square inch (psi) 1380 megaPascals (MPa), (b) good heat resistance as exhibited by a heat distortion temperature under load of at least 100.degree. F. at 66 psi or 37.degree. C. at 0.45 MPa, and (c) good low temperature toughness as exhibited by a notched Izod impact resistance of at least 5 foot pounds per inch (ft lbs/in) at -30.degree. F. or 49 Joules per meter (J/m) at -34.degree. C. More preferably a thermoplastic resin will have a modulus value of less than about 175,000 psi (1200 MPa), a heat distortion temperature under load of at least 120.degree. F. (49.degree. C.) at 66 psi (0.45 MPa), and a notched Izod impact resistance of at least 5 ft lbs/in (49 J/m) at -40.degree. F. (-40.degree. C.).